1. Field of the Invention
The present invention is related to a radiation image detecting apparatus equipped with a radiation image detector that records radiation images, by generating electric charges when irradiated by recording electromagnetic waves that bear radiation images, and accumulating the generated electric charges. The present invention is particularly related to a radiation image detecting apparatus which is further equipped with a light emitting means for emitting light onto the radiation image detector during irradiation of the recording electromagnetic waves.
2. Description of the Related Art
Various types of radiation image detectors that record radiation images of subjects when irradiated by radiation which has passed through the subjects have been proposed and are in practical use, in the field of medicine and the like.
There are radiation image detectors that utilize amorphous selenium that generate electric charges when irradiated by radiation. Radiation image detectors of this type that employ the TFT readout method have been proposed.
A radiation image detector that employs the TFT readout method and is constituted by: a biasing electrode, to which a biasing voltage is applied; a photoconductive layer for generating electric charges when irradiated with radiation; and an active matrix substrate, in which a great number of pixels that include charge collecting electrodes for collecting the electric charges, which are generated in the photoconductive layer, accumulating capacitors for accumulating the electric charges collected by the charge collecting electrodes, and TFT switches for reading out the electric charges, which are accumulated in the accumulating capacitors, are arranged two dimensionally, are laminated, for example, has been proposed.
In the TFT readout type radiation image detector having the construction described above, radiation which has passed through a subject and bears a radiation image is irradiated onto the radiation image detector from the side of the biasing electrode, in a state during which a positive voltage is being applied to the biasing electrode from a voltage source, to record the radiation image.
The radiation which is irradiated onto the radiation image detector passes through the biasing electrode, and is enters the photoconductive layer. The radiation causes charge pairs to be generated in the photoconductive layer. Among the generated charge pairs, negative electric charges combine with the positive electric charges which are charged in the biasing electrode, and disappear. Meanwhile, positive electric charges from among the generated charge are collected by the charge collecting electrodes of each pixel of the active matrix substrate, accumulated in the accumulating capacitors, and recorded as a radiation image.
The TFT switches of the active matrix substrate are turned ON according to control signals output from a gate driver, to read out the electric charges which are accumulated in the accumulating capacitors. The electric charges are amplified as charge signals by a charge amplifier and detected, to read out image signals corresponding to the radiation image.
In radiation image detectors that employ active matrix substrates as described above, no electrodes for discharging electric charges are provided in the spaces among the charge collecting electrodes which are divided for each pixel. Therefore, the electric charges which are generated due to the irradiation of radiation tend to accumulate within these spaces. As a result, the electric fields which are formed within the photoconductive layer become distorted, causing the problems that the sensitive area of the photoconductive layer changes, and that the sensitivity thereof varies. In addition, there is a problem that the electric charges which have accumulated in the spaces among the charge collecting electrode leak out during readout of charge signals after irradiation of radiation is ceased. The leaked electric charges are output as residual images, causing residual image properties (lag properties) to deteriorate.
To address the above problems, radiation image detecting apparatuses equipped with light sources for emitting back light from the active matrix substrate side of radiation image detectors has been proposed (refer to U.S. Pat. Nos. 6,995,375, and 7,034,312, for example). Electric charges can be accumulated in the spaces among charge collecting electrodes in advance by emitting the back light onto the radiation image detector during irradiation of radiation. Thereby, electric fields which are formed within a photoconductive layer can be distorted in advance. Accordingly, the electric charges which are generated due to the irradiation of the radiation do not accumulate within the aforementioned spaces, move along the electric fields which are distorted in advance, and are collected by the charge collecting electrodes. That is, change in the sensitive area of the photoconductive layer, and the variation in the sensitivity thereof can be suppressed. In addition, the electric charges that leak out from the spaces among the charge collecting electrodes can be prevented from being output as residual images, by continuing to emit the back light after irradiation of the radiation has ceased.
U.S. Pat. Nos. 6,995,375, and 7,034,312, also proposes a radiation image detector provided with an intermediate layer formed by Sb2S3 between the photoconductive layer and the active matrix substrate. The amount of back light which is emitted into the photoconductive layer can be decreased by providing the intermediate layer, thereby suppressing generation of dark current within the photoconductive layer.
However, an intermediate layer formed by Sb2S3 cannot sufficiently absorb back light, and generation of dark current within the photoconductive layer due to emission of the back light thereon remains a problem.